Joy Milne’s husband Les died at 65 earlier this year, following 20 years of living with the disease.

"I've always had a keen sense of smell and I detected very early on that there was a very subtle change in how Les smelled,” Mrs. Milne, 65, told STV News. “It's hard to describe but it was a heavy, slightly musky aroma. I had no idea that this was unusual and hadn't been recognised before.

"I watched with interest how research had uncovered distinctive smells associated with certain diagnoses and when I was attending a Parkinson's UK research lecture at the University of Edinburgh a few years ago I mentioned it to the researcher, Dr. Tilo Kunath,” she continued. "Tilo was interested and together we worked out ways to see if I could detect it from other people with Parkinson's and not just Les. It turned out I could."

Researchers believe that Parkinson’s may result in a change in the sebum, an oily substance in the skin, that leads to a particular smell.

A new study, funded by Parkinson’s UK, will take skin swabs from around 200 people in Manchester, Edinburgh and London, both with and without Parkinson’s. The researchers hope to be able to find a molecular signature responsible for the odour in people with Parkinson’s and use this to create a diagnostic test, which could be as simple as wiping someone's forehead with a swab.

To back up the testing process people with exceptional smelling abilities, like Mrs. Milne (known as “human detectors”) will also be involved.

Amazingly Mrs. Milne was able to identify people who had Parkinson’s simply by sniffing the T-shirts they had slept in. The first time she was tested at Edinburgh University, she correctly identified that seven people had Parkinson's (including one control subject who wasn't diagnosed for another eight months) and five other people didn't.

Professor Perdita Barran, leading the research at the Manchester Institute of Biotechnology, said: "It is hoped that these results could lead to the development of a non-invasive diagnostic test that may have the ability to diagnose early Parkinson's — possibly even before physical symptoms occur."

One in 500 people in the U.K. has Parkinson's for which there is no definitive diagnosis and no cure. For more information about Parkinson's visit Parkinson's UK.